Method of and means for controlling alternating-current motors.



O. E. LORD.

METHOD OF AND MEANS FOR CONTROLLING ALTBRNATING CURRENT MOTORS.

APPLIOATIOH FILED we. 21, 1906. nmznwnn SEPT. 11, 1908.

1,1 1 5,948. Patented Nov. 3, 19M

INVENTOR amino 1 STATES PATENT orrion.

CHARLES E. LORD, OF NOBWOOD, OHIO.

' mn'rnon or AK!) nuns roa oon'raoLnrno ALrnnNArmG-oUnnnNr MOTORS.

Specification of Letters Patent.

' Patented Nov. 3, 1914.

Application filed August 27, 1908,'Ser1a1 No. 882,183. Renewed September11, 1908. Serial No. 452,661.

To all whom it-may concern:

Be it known that I, CHARLns E. LORD, citizen of the United States,residing at Norwood, in the county of. Hamilton and State of Ohio, haveinvented certain new and useful Improvements in Methods of and Means forControllin Alternating-Current Motors, of which the ollowing is a full,clear, and exact specification. I My invention relates to motor controlsystems and particularly to control systems for alternating current milland .holsting motors.

In rolling mills and in mine hoisting machinery it is necessary that themoving parts be .quickly and'often reversed. -Heretofore steam engineshave generally been used for this work, but these have been cumbersomeand complicated, their operation has been uneconomical, and theircontrol has been extremely difiicult and altogether unsatisfactory. aThe object of my ing mills and mine hoisting machinery. This isaccomplished b means of an economically operated an mo-electric'machines.

In one aspect my present invention comprises the method of operating aninduction "motor at variable s eed which consists in inversely varying te potential impressed upon its primary member and the resistance of itssecondary member.

. comprising a. source of current, a motor sup- 7 plied thereby, afly-rwheel mechanically connected to said motor, an alternating currentgenerator driven b said motor,an induction motor supplie by. saidgenerator, and meansfor inversely varying the field strength "of saidalternating current generator and present-invention is to simplify theoperation and control of rollreadil-y controlledarrangementofalternating current dynamachines B and D may the resistance of thesecondary circuit of three-phase induction type, thou h obyiously otherforms of motors could e used instead. In the rotor circuit of this motoris a starting resistance 1 adjustable by means of a short-circuiting bar2, and are lating resistance 3 arranged to be cut in an ou't by a.solenoid switch 4, which in turn is responsive to the current strengthin the primary circuitof the motor,as through a series transformer 5.Other means for varyin the speed of motor'A may be used if desire .Thearmature of .a three-phase alternating current generator B is driven bythe motor A, being preferably directly connected thereto, and-on the.common shaft of the .motor A and generator B is a heavy flywheel G. Thegenerator B supplies current to the primary member of a working motor Dof the three-phase induction type. The motor-D may be used to drive anydesired machinery. Although the generator B and the motor I) are shownas three-phase machines it is obvious that my invention is not limitedto this number of hases but'that the e wound for any number of phases;and it isnot necessary that the motor D be an induction motor, as othertypes of alternating current motors may be used.

The field coil 6 of generator B is supplied by an exciter E,'having aself excited field e,

the strength of which can be controlled by therheostat 12. 'Any otherdirect current source'may be used to supply the field coil 6.

The controller H is arranged to control the resistance 14: in thecircuit of the field coil 6 and also'the resistances 15, 16 and 17 inthe secondary or rotor circuit of the workingmotor D. The two ends oithe arm 7:. of the controller H are electrically distiiict, and'c'ontrolthe resistance 14, and the re of the drawings shows I resistances 15, 16and 17 respectively. As shown, a movement of handle it variessuccessively the two sets of resistances, first cut ting the resistance14 out of the field circuit 2) and then cutting the resistances 15, 16and y 17 out of the secondary circuit of the motor D. The cutting out ofresistance 14 increases the otential of generator B thereby increasing te speed of motor D in the man: ner of the well known otential starter.The cutting out of the resistances 15, 16 and 17 further increases thespeed of 'motor D, by

; decreasing the resistance of the circuit of the f. A s ring-pressed Anon-inductive resistance 13 is connected in series with the field coil6. This resistance has an ohmic value several t1mes as great as that ofthe field coil with which it is in series. The purpose of thisresistanceis to diminish the time constant of the field magnet b, for the timeconstant of a circuit is a function of its inductance divided by itsresistance. Therefore by increasing the resistance. of the field circuitwithout increas: ing its inductance, the current strength he- 1 ing keptthe same, the time constant of the field magnet is greatly reduced. Bythis more readily obtained.

-means quick reversals of the motor D may be The operation of the systemis as follows :-The primarycircuit of motor A is closed "and the motorstarted by movingbar 2 to cut out the starting resistance 1. The switch4 is held open b its solenoidat this time because of the heavy currentrequired for starting) the motor. If desired, other means may e used toinsure the open condition of this switch durin starting. After the motorhasgained sufllcient speed and the l starting resistance has been cutout, the sole- 1 mechanical energy by its rotation.

noid switch is allowed to close to cut out resistance- 3 because of thedecrease inthe primary current of motor A. The fly-wheel C and thegenerator armature B are also started with the motor A and the fly-wheelstores Duringthis starting the arm 7 is preferably in the position inwhich all the resistance It is in circuit or the circuit including suchresists preferably open. Thehandlefisnow moved to close switch F in theproper position-to. giv'e the motor D the desired (hrection of I ance isopen, and the reversing. switch F is rotation, and the arm his moved ina clockwise direction. The movement of the arm h gradually cuts theresistance 14 out of. circuit with coil 12, thereby increasing theelectromotive vforce impressed u on the primary member of the motor D.hen the entire resistance 14 has been cut out of circuit the field coil6 is at its strongest and the electromotive force impressed by thearmature of enerator B upon the motor D has reached 1ts maximum. So farthe resistances 15, 16 and 17 in the secondary circuit of motor D haveremained unchanged. After resistance 14 hasbeen fully out out, afurthermovement of arm h graduall cuts the resistances 15, 16 and 17 outof their circuit and diminishes the resistance of the secondary memberof motor D, thereby diminishing the slip of said motor. The cutting outof resistance 14 and of the resistances 15 16 and 17 both increase thespeed of motor .D. The speed which this motor acquires depends upon theextent of movement of the arm h, the full speed bein reached when theresistances 15,

1 16 and 17 have been fully cut out of circuit.

If the load on the working motor increases,

1 said'motor requires more power for its operation than the motor A canfurnish. The

' current rising in the primary of transformer by reason of thisheavy-load, the switch 4 is opened, thus inserting resistance 3 into therotor circuit of motor A. This increases the slip of motor A and permitssaid motor to slow down, thus allowing the fly-wheel Oto jgive up someof the energy it has stored, @which energy helps the motor A to drivethe generator B to supply electrical energy at the rate demanded by themotor D to i drive its load.

. As the arm 72. is moved backward or in a counter-clockwise direction,the resistances 'i 15, 16 and 17 are first cut into the secondarycircuit of the working motor to increase the slip thereof, and then theresistance 14: is cut iinto circuit with the field coil 6. Both of.these changes allow the motor D to slow down. The diminished current inthe pri- 'mary of transformer 5 also'causes the sole Qnoid switch 4 toclose, thereby increasing the ;speed of motor A so that the latter mayagain supply energy to the fly-wheel C. The fiy-wheel thus stores up anexcess of energy sup lied when "the rate 0 such supply excee s the rateat which energy is demanded ;by the working motor, and gives up saidflstored energy whenever the rate of energy demanded is greater than therate of energy supplied. .When the arm 12. has been moved ;-as far aspossible counter-clockwise the switch F is released from its catch 10and can be thrown to its otherposition to reverse the motor D, when theabove cycle may be repeated, save that the motor-D isceumd .to rotate intheother direction.

When I use the term i inversely in this description and in the claims I-do not wish to limit myself to exact inverse proportion, but intend theterm to include any increase in one and decrease in the other of the twothings specified.

I have described my invention in what I now consider its preferred formbut I intend to cover in the claims all those obvious modificationswhich readily occur to one skilled in the art,

Having thus described my inventiomwhat I claim as new and desire tosecure by Letters Patent is 1. The method of operating an alternatmgcurrent motor at variable speed, which consists in inversely varying thepotential impressed upon its primary member and the resistance of thecircuit of its secondary member.

2.v The method of operating an induction motor at a variable speed,which consists in successively and inversely varying the otentialimpressed ;:upon its primary memher and the resistance of the circuit-ofits secondary member.

3. The method of operatin an induction motor at variable s eed, WlllChconsists in inversely varying t e potential impressed upon its primarymember and the resistance 9 the circuit of its secondary member, stor Inas mechanical energy any excess of supphed energy when the load on themotor is light, andsu lyin said stored ener tothe motor ase l ctricfilenergy when the l oad on. the motor is heavy.

4. The method of operatin an alternating current motor at variabde speedand load, consistin in successively and inversely varying the eectromotive force applied to its primary member and the resistance ofthe circuit of its secondary member, storing as mechanical ener theexcess of energy when the supplie power exceeds the power demanded bythe load and supplying said stored energy to the motor as electricalenergy when the power demanded by the load exceedsfthe supplied power.

5. A system of motor control, comprising an alternating current motor, agenerator for supplying said motor, and means for tive force of saidgenerator and the resistance of the secondary circuit of said motor.

7. A system of motor control,comprising an induction motor, a generatorfor supplying said motor, resistances in the field circuit of saidgenerator and the secondary circuit of said motor respectively, and aunitary means for varying said resistances.

- an alternating current motor, an alternating current generator forsupplying said motor, resistances associated with said generator andsaid motor respectively, a single means for controlling saidresistances, and a reversin switch for said motor arranged to be 100 edagainst movement save when the resistance associated with the generatoris all in circuit.

10. A s stem of motor control, comprising'an induction motor, analternating current generator for supplying said 1notor,'resistances inthe field circuit of said genera tor and the secondary circuit of saidmotor respectively, a reversing switch for said motor, and means forlocking said reversing switch save when the resistance in the generatorfield circuit is a maximum.

11. A system of motor control, comprising an alternating current motor,a generator for supplying said motor, means for varying theelectromotive force of the generator and the resistance of the secondarycircuit ofsaid motor, a reversing switch for said motor and means forlocking said reversing sw tch save when the electromotive force of thegenerator is a minimum.

12. A system of motor control, comprising an alternating current motor,a generator for supplying said motor, means for successively andinversely varying the electromotive force of said generator and theresistance of the secondary circuit of said motor, and a fly-wheelmechanically connected to said generator.

13. In combination, a source of power, an alternating current generatordriven thereby, a fly-wheel mechanically connected to the generator, analternating current motor supplied by said generator, and means forinversely varying the electromotive force of said generator and theresistance of the secondary circuit of-said motor.

14. In combination, a sourcev of current, a motor supplied thereby, afly-wheel mechanically connected to said motor, an alternating currentgenerator driven by said motor, an induction motor supplied by saidgenerator, and means for inversely varying the field strength of saidalternating current generator and the resistance of the secondarycircuit of said induction motor.

15. In combination, a source of power, an alternating current generatordriven thereby, an induction motor supplied by the generator, means forsuccessively varying resistances in the field circuit of the generatorand the secondary circuit of the motor res ectively, a fiywheel on thegenerator s aft, and means for allowing said fiy-Wheel to give up itsenergy when the motor load rent generator drivemthereby, a fly-wheel onthe shaft of said induction motor, an alternating current working motorsupplied by said generator, and means for successively and inverselyvarying the field strength of the generator and the resistance of thesecondary circuit of the working motor.

18. A s stem of motor control, compris-' mg an 1n uction motor, analternating cur-' rent generator driven thereb a fly-wheel on the shaftof said induction motor, an alternating current working motor suppliedby said generator, means for successively and inverselyvarying the fieldstrength of the generator and the resistance of the secondary circuit ofthe workingmotor, and means for increasin the slip of the inductionmotor when a eavy load is placed on the working motor.

19. A system of motor control, compris ing an alternating currentmotor,an alternating current generator'suppl ing said motor, means for.varying the e ectro motive force of said generator,'a reversing'switchfor said motor, and means for preventing the operation of said reversinswitch save when l the electro-motive force said generator is a minimum.

. 20. A system ing an alternating current motor, an a ter nating currentgenerator for sup lyin said motor, resistances associated wit sal gen-1erator and said motor; respectively, single means for controlling saidreslstances, and a reversing switch for said motor arranged to be lockedagainst movement save, when the resistance associated'withthe motor,-is

- all in circuit.

in means for reversing'the circuit connections of said motor, saidreversing, means belng i' m; "is-operable,

its

21. A system of mdtor control, comprisa ing an alternating currentmotor, an alternating current-generator for supplying'said motor unitarymeans for vary ng the volt age of the secondary circuit of said motor,and

"nly whenthe maximum, motor slip exists underrnormal operating conditimeI 22. A system of motor control; comprisof motor control, com ris saidgenerator and effective resistance ing an alternating current motor, analternatmg current generator for supplying said motor, unitary means forvarying the volt-' age of said generator and effective resistance in thesecondary circuit of said motor, and means controlling the direction ofrotation of said motor, said controlling means being operable only whenthe maximum motor slip exists under operating conditions. i

23. A system of motor control, comprising an alternating current motor,an alternating current generator for supplying said motor, unitary meansfor varying the voltage of said generator and effective resistance inthe secondary circuit of said motor, and means for reversing circuitconnections of said motor, said reversing means being rendered operableby said unitary means.

24. A system of motor control, compris ing an alternating current motor,an alter-' nating current generator for supplying said motor, unitarymeans for'varyi-ngthe voltage of said generator and efiective;resistance in the secondary circuit of said more}; and means forcontrolling the directidn' 'of rota tion of said motor, said controllingmeans being rendered operable by said) unitary means.

25. A system 'of motor control, comprismg an alternating currentmotor,an a ternating current generator for supplyin said motor,resistances associated with'sai generator and said motor respe'tively,single means for controlling said refisistances, and a reversing switchfor said motor arranged to be locked against movementsave when theresistance associated with the motor is all in circuit, said reversingswitch being controlled by said single means. a

26. A system of motor control, comprising an alternating current motor,an a nating current'generator for sup said .motor, resistancesassociatedwit sai generator and said motor res ectively, unitary {meansfor controlling sai resistances, and a reversing'switc'h forsaid motor]being rendered operative by said unitary" means uni der certainpredetermined conditions. and being arranged to be locked against move:ment save when the resistance associated with said motor is all incircuit.

27. A systemfof motor control, comprising an alternating currenflmotor,a generator for su plying said'motor', means for varying thee eratjorand the resistance of the secon ary circuit fof said" motor, and: meansadapted to i be controlled by "said'first mentioned means iforcontrolling the direction of rot'ation of said-motor. ianalternating'current motor, a generator for supplyingsaid motor means forvarying the electromotivegforce o said-generatorand Rthfi resistance ofthe secondary circuit of said ter-' ectromotive force ofs'aid en-"motor, and a reversing switch for said motor adapted to be controlled bysaid means for controllingthe direction of rotation of said motor.

29. A system of motor control, comprising an alternating current motor,a generator for supplyin said motor, unitary means for varying t eelectromotive. force of said generator and the resistance of thesecondary circuit of said motor, a reversing switch adapted to becontrolled by said uni-. tary means for controlling the direction ofrotation of said motor.

30. A s stem of motor control, comprising an in uction motor, analternating current generator for supplying said motor, means forinversely varying the electromotive force of said generator and theresistance of the secondary circuit of said motor, and means adapted tobe controlled by said first mentioned means for controlling thedirection of rotation of said motor.

31. ,A system of motor control, comprising an induction motor, agenerator for supplying said motor, resistances in the field circuit ofsaid generator and thesecondary circuit of-said motor respectively,unitary means for varying said resistances, and means adapted to berendered operative by said unitary means for controlling the directionof rotation of said motor.

32. A system of motor control, compris- 1ng an induction motor, agenerator for supplying said motor, resistances in the field v circuitof said motor res circuit of said generator and the secondary means forvarying said resistances, and a reversing swltch for said motor adaptedto be controlled by said unitary means under certain predeterminedconditions.

33. A system of motor control, comprising an induction motor,an-alternating current generator for sup. lying said motor, reslstances1n the field circuit of said generator and the secondary circuit of saidmotor respectively, unitary means for varying said res stancesrespectively, and means adapted tobe controlled by said unitary meansfor controlling the direction of rotation of said motor.

. 34. In a system of motor control, comprismg an alternating currentmotor, an alternating current generator for supplyin said motor,resistances associated with sai generator and said motor respectively,single means for controlling said resistances, a reversing switch forsaid motor adapted to be operated only when the resistance associatedwith the generator is all in circuit.

35. A system of motor control, comprising an induction motor analternating current generator for supplying said motor, resistances inthe field circuit of said generator and the secondary circuit of saidmotor respectively, a reversing switch for said ctively, unitary motor,and means. adapted to operate said switch only when the resistance inthe generator field circuit is a maximum.

36. A system of motor control, comprising an alternating current motor,a generator for. supplying said motor, means for varying theelectromotive force of the generator and the resistance of the secondarycircuit of said motor, a reversing switch for said motor, and meansadapted to operate said switch only when the electromotive force of thegenerator is a minimum.

37. A system of motor control, comprising an alternating current motor,a generator for supplying said motor, means for successively andinversely varying'tlie electromotive force of said generator and theresistance of the secondary circuit of said motor, means for controllingthe direction of rotation of said motor and adapted to be renderedoperative by said first mentioned means, and a fly-wheel mechanicallyconnected to said generator.

38. In combination, a source of power, an alternating current generatordriven thereby, a fly-wheel mechanically connected to the generator, analternating currentmotor supplied by said generator, means for in--versely varying the electromotive force of said generator and theresistance of the secondary circuit of said motor, and means forcontrolling the direction of rotation of said motor and adapted to berendered operative by said first mentioned means.

39. In combination, a source of current, a motor supplied thereby, afly-wheel mechanically connected to said motor, an alternating currentgenerator driven by said motor, an induction motor supplied by saidgenerator, means for inversely varying the field strength of saidalternating current generator and the resistance of the secondarycircuit of said induction motor, and

shaft, and means for allowing said fly-wheel to give up its energy whenthe motor load rises above normal.

41. A system of motor control, comprising an alternating currentgenerator, an alternating current motor supplied thereby, means forsuccessively varying the field strength of said generator and theresistance of the secondary circuit of said motor,

a amnes a means for controlling the direction of rotation of said motorand adapted to be rendered operative by, said first mentioned means, anda resistance permanently in the field circuit of said generator.

42A system of motor control, comprising an induction motor, analternating cur rent generator driven thereby, a fiy-wheel on the shaftof said induction motor, an al- I ternating current working-motorsupplied by said generator, means for successively and inversely varyingthe field strength of the generator and the resistance of the sec-'ondarycircuit of the working motor, and

means for controlling the direction of rotation of said motor andadapted to be controlled by said first mentioned means.

43. system of motor control, compris; mg an m uction motor, analternating cur- 7 ondary circuit of the working'motor, means forcontrolling the direction of rotation of said motor and adapted to berendered operative b said first mentioned means, and means or increasingthe slip of the induction motor when a eavy load is placed on theworking motor.

In testimony whereof I a fix my, signature,

in the presence of two witnesses.

CHARLES E. LORD.

Witnesses: I RUBY Bonmson, 1 Fan J. KINBEY.

